The present invention relates to a surveying method, a surveying system, and a surveying data processing program for acquiring three-dimensional data of a predetermined area.
In recent years, three-dimensional surveying on three-dimensional object has been more frequently performed, and there are now growing demands on an image with three-dimensional data to be used for an electronic map. Because of such circumstances or the like, the amount of the data required for surveying purpose has extensively increased.
A laser scanner is known as a surveying system for measuring a large amount of three-dimensional data in detail and within short time.
A laser scanner is a surveying system for projecting a pulsed laser beam to a predetermined measurement area, for receiving a reflected light of the pulsed laser beam to measure three-dimensional position data at a projecting point of the pulsed laser beam for each pulse, and for acquiring point cloud data of the measurement area.
The laser scanner can obtain a large amount of point cloud data within short time. However, when obstacle(s) such as a vehicle, a tree, etc. are present in the measurement area, shadow (occlusion) occurs, and this causes a portion where the data is lacking. Also, because a distance is measured by the reflection of a pulsed laser beam, if reflectivity at the projecting point is low, e.g. if the laser beam used is in green color when the reflection point is in black color or in complementary color (i.e. in red color), the reflected light cannot be obtained. This causes a data-lacking portion to occur, too.
Further, when the measurement area is scanned from a horizontal direction, point cloud data cannot be obtained on the upper surface of a building or a structure, for instance.
For the purpose of obtaining point cloud data of the portion in occlusion, it has been practiced to move the laser scanner and to acquire the data of the portion in occlusion. Also, in order to obtain the point cloud data on the upper surface of a building or a structure, the laser scanner is moved to a position where the upper surface can be projected by the laser beam from the laser scanner to acquire the point cloud data on the upper surface.
For this purpose, every time the occlusion portion occurs, the laser scanner had to be moved. Or, large-scale equipment or tools such as a scaffold or an elevator or the like had to be installed to move the laser scanner to higher position. This means that tremendous efforts and long time are required for the surveying operation.
Also, when reflectivity is low at the point to be measured, such inconveniences often arise that the point cloud data cannot be obtained.